The present invention relates to a screw pump unit.
As disclosed in the official gazette of Japanese patent application Laid-open No. 60-216089 (the specification of U.S. Ser. No. 701,199), a prior-art screw vacuum pump is such that a pair of male and female rotors which rotate meshing with each other are received in the working chamber of a casing which has suction ports and discharge ports, and that the rotors are driven by a driver, whereby a gas is imbibed from a space to have its pressure lowered, into the interstice between both the rollers, and it has its pressure raised and is exhausted into the atmosphere.
In the prior-art unit, the axes of the male rotor and female rotor are arranged within a horizontal plane, and both the rotors are arrayed within the horizontal plane, so that a floor area required for installation enlarges. Moreover, on account of the structure in which the suction ports and discharge ports of the casing are arranged on both the sides of tne horizontal plane (in the upper surface of the casing and the lower surface thereof), either the suction ports or the discharge ports are lie in the lower surface of the casing. Therefore, the job of connecting pipes to the suction ports or the discharge ports lying in the lower surface of the casing must be carried out at the lower surface of the casing, and the job efficiency is very inferior. Further, in a case where reaction products have deposited in the vacuum pump as in use for the evacuation of a semiconductor manufacturing plant, it is not easy to eliminate the products or to routinely inspect the situation of deposition. In performing these operations, there are the problems that pipes need to be detached and that special tools are required.